Massive MIMO multi-user beamforming and single channel full duplex for wireless networks

ABSTRACT

This invention presents a method and apparatuses for wireless networking comprising one or more BS with N bs  antennas; two or more SCs in the range of a BS where a SC has N sc  antennas, uses N sc1 ≦N sc  antennas for communication with a BS and uses N sc2 ≦N sc  antennas for communication with one or more UEs; at the same time a BS transmitting DL signals to K SCs using multi-user transmit BF in a frequency channel, a SC simultaneously transmitting DL signals to one or more UEs in its range using the same frequency channel; and, at the same time a BS receiving UL signals from K SCs using multi-user receive BF in a frequency channel, a SC simultaneously receiving UL signals from one or more UEs in its range using the same frequency channel. Furthermore, beamforming using antennas on the SCs is performed to reduce the inter-SC interferences.

This application claims the benefit of U.S. Provisional Application No.61/905,260, filed on Nov. 17, 2013.

TECHNICAL FIELD

The present application relates to methods for wireless networking toincrease throughput over given radio frequency (RF) bandwidth and toapparatus and systems that implement the methods, and more specificallyto methods and related apparatus and systems that applies beamforming(BF) in a base station with a large number of RF chains and antennas anduses single channel full duplex radios on an infrastructure node in thenext tier, e.g., pico cells.

BACKGROUND

Massive MIMO multi-user Beamforming (MM-MUBF) offers the potential tosignificantly increase the spectral efficiency and throughput by manyfolds through spatial multiplexing. However, when the number of RFchains and antennas becomes large (It is understood that an antenna isassociated with a RF chain, transmit (Tx) or receive (Rx), thus,hereafter when the number of antennas is used, it should be understoodto mean the number of antennas and the associated RF chains), there aresignificant overhead in channel estimation to obtain Channel StateInformation (CSI). This problem becomes more challenging if the channelcoherence time is short, e.g., in the case of a Base Station (BS) with alarge number of antennas communicating with a fast moving User Equipment(UE) because a large number of channels need to be estimated frequently,reducing the time left for actual data communication. This problem isfurther compounded by the number of fast moving UEs. On the other hand,the industry is moving towards Small Cells (SC) and HeterogeneousNetwork (HetNet) as a way to meet the fast increasing data traffic.Ideally, the placement of SCs should be determined by the data trafficneeds, not constrained by the availability of wired connection to thebackhaul network. MM-MUBF is a good match for this need as it canprovide high capacity wireless backhaul for many SCs so they can beplaced at any place there is a power plug. Since the channels between aBS and SCs are very slow varying, the need for frequent estimation ofCSI is alleviated.

However, prior art uses out-band wireless backhaul, meaning thatdifferent frequency ranges are used for the backhaul between BS and SCand for the communication with UEs. This requires precious frequencyresources, which may not be available especially at low frequencies (afew GHz or lower), and even if they are available, they should be usedto increase the data throughput with the UEs. In addition, lowfrequencies wireless backhaul is desired because it does not requireline of sight, and offers better penetration than high millimeter wavefrequencies. Thus, in-band wireless backhaul, meaning using the samefrequencies for the communication with UEs to provide the wirelessbackhaul between BS and SCs, is desired. This requires a SC tosimultaneously transmit and receive in the same frequency channel,referred to as Single Channel Full Duplex (SCFD).

The terms BS and SC will be used to mean either the radio apparatus fortransmitting and receiving signals in a cell or the area covered by suchradio apparatus, as evident from the context. The term BS is used tomean a cell coverage area much larger than a SC. In the terminology of4G LTE, both a BS and a SC in this application can be a “small cell”, aSC being a tier below a BS, e.g., a BS below may be a microcell in 4GLTE terminology and SC may be a pico cell in 4G LTE terminology.

This invention presents embodiments that solve the technical challengesdiscussed above.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A and 1B show the network traffic in the downlink and uplinkdirections respectively for a TDD network.

FIG. 2 shows the flowchart for a BS to decide whether a UE should beincluded in MFD-SC-IS.

FIG. 3 shows the network traffic in the downlink and uplink directionsfor a FDD network.

FIGS. 4A and 4B show the network traffic in the downlink and uplinkdirections respectively for a FDD-TDD network.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

Reference may now be made to the drawings wherein like numerals refer tolike parts throughout. Exemplary embodiments of the invention may now bedescribed. The exemplary embodiments are provided to illustrate aspectsof the invention and should not be construed as limiting the scope ofthe invention. When the exemplary embodiments are described withreference to block diagrams or flowcharts, each block may represent amethod step or an apparatus element for performing the method step.Depending upon the implementation, the corresponding apparatus elementmay be configured in hardware, software, firmware or combinationsthereof.

One embodiment of this invention is a method for wireless networking, orthe apparatus that implement this method, comprising one or more BS withN_(bs) antennas, two or more SCs in the range of a BS where a SC hasN_(sc) antennas and may use N_(sc1)≦N_(sc) antennas for transmitting orfor communication with a BS and N_(sc2)≦N_(sc) antennas for receiving orfor communication with one or more UEs, and one or more UEs in the rangeof a SC and each UE has up to N_(ue) antennas; at the same time a BStransmits downlink (DL) signals to K SCs using multi-user transmit BF ina frequency channel where K>1 and N_(bs)>KN_(sc1), a SC simultaneouslytransmits DL signals to one or more UEs in its range using the samefrequency channel; and, at the same time a BS receives uplink (UL)signals from K SCs using multi-user receive BF in a frequency channelwhere K>1 and N_(bs)>KN_(sc1), a SC simultaneously receives UL signalsfrom one or more UEs in its range using the same frequency channel. Notethat the same antennas on a SC may be used simultaneously for DL and UL,i.e., there are total N_(sc)=N_(sc1)=N_(sc2) antennas and each is usedfor both Tx and Rx simultaneously, e.g., through a circulator. FIG. 1shows an example of a network operated in Time-Division Duplexing (TDD)mode of this embodiment with one BS 1, K=5 SCs 2 and one or more UEs 3in each SC. FIG. 1A shows the network traffic in the downlink directionwhich includes the BS-SC links 4 and the SC-UE links 5, and FIG. 1Bshows the network traffic in the uplink direction which includes theUE-SC links 6 and SC-BS links 7. As can be seen form FIG. 1, in eitherdirection, the SC is required to simultaneously transmit and receive inthe same frequency channel. Such a SC is referred to as working inSingle Channel Full Duplex (SCFD) mode. This embodiment is referred toas MFD-SC (MUBF single channel Full Duplex Small Cell). Full DuplexSmall Cell requires self-interference cancellation, that is, cancelingthe interference to the SC's receiver caused by the Tx signals from itstransmitter. This self-interference cancellation can be performed usinga RF filter that generates a RF cancellation signal to subtract theself-interference from the received RF signal prior to the Low NoiseAmplifier (LNA) of the receiver to avoid saturating the LNA. It mayfurther be canceled by generating an analog cancellation signal inanalog baseband or IF (intermediate frequency) to avoid saturating theADC. What is remaining of this interference may further be canceled indigital baseband signal processing techniques. A combination of thesecancellation techniques can avoid saturating the LNA and the ADC, andimprove the SINR sufficiently to achieve the desired data rate.

In the descriptions below, without loss of generality, we assume eachBS, SC and UE in the network has the same number of antennas andN_(sc)=N_(sc1)=N_(sc2) for simple presentation. The description can beeasily modified to different numbers of antennas for the BSs, SCs andUEs and N_(sc1)<N_(sc) or N_(sc2)<N_(sc) without changing the nature ofthe description.

Let the channel from a BS to the K SCs be denoted by a KN_(sc)×N_(bs)matrix H_(b-s), the channel from a SC to its UEs be denoted by aMN_(ue)×N_(sc) matrix H_(s-u), and the channel from a BS to the UEs bedenoted by a KM N_(ue)×N_(bs) matrix H_(b-u), where M is the number ofUEs served simultaneously by a SC in the same resource block. Withoutloss of generality, we assume M=1 in the description below.

In the downlink direction, multi-user transmit BF can provide power gainover the entire available bandwidth for each SC while eliminating orsignificantly reducing the interference from the multiple streams. Itcan be achieved using either the Zero Forcing (ZF) method, the ConjugateBeamforming (CB) method or other methods for beamforming. ZF is usedbelow for the description of the embodiments. With ZF BF, the BF matrixB_(d)=[H_(b-s) ^(H)(H_(b-s)H_(b-s) ^(H))⁻¹] is the pseudo-inverse andthe received signal y_(sc) by the SCs is given byy _(sc) =H _(b-s)[H _(b-s) ^(H)(H _(b-s) H _(b-s) ^(H))⁻¹]S _(d) x _(bs)+n _(sc) =S _(d) x _(bs) +n _(sc)  (1)where x_(bs) is the signal transmitted by the BS to the K SCs, n_(sc) isthe noise vector at the SC, and S_(d) is a power scaling matrix which istypically diagonal.

In the uplink directions, multi-user receive BF can be achieved using ZFwith BF matrix B_(u)=[(H_(b-s)*H_(b-s) ^(T))⁻¹H_(b-s)*] and the receivedsignal y_(bs) by the BS is given byy _(bs)=[(H _(b-s) *H _(b-s) ^(T))⁻¹ H _(b-s)*]H _(b-s) ^(T) S _(u) x_(sc)+[(H _(b-s) *H _(b-s) ^(T))⁻¹ H _(b-s)*]n _(bs) =S _(u) x _(sc) +B_(u) n _(bs)  (2)where x_(sc) is the signal transmitted by the K SCs to the BS, n_(bs) isthe noise vector at the BS, and S_(u) is a power scaling matrix which istypically diagonal.

In SCFD, the same frequency band is used for both UL and DL. Therefore,the DL and UL channels can be considered reciprocal after calibration oftransfer functions of the Tx and Rx chains. This channel reciprocity canbe used to reduce the overhead in channel estimation needed for BF. A BScan estimate H_(b-s) by having SCs transmits pilot signals.

In the downlink direction, when the BS is transmitting to SC(s) while aSC is transmitting to a UE, the BS→SC transmission causes interferenceto the UE. One embodiment adds interference suppression to MFD-SC,referred to as MFD-SC-IS (MFD-SC with Interference Suppression) byadding a null space pro-coding matrix to suppress this interference.This is doable when N_(bs) is much larger than the number of totalantennas on all the UEs in the range of the BS. Assuming the totalnumber of antennas on all the UEs is K N_(ue) and N_(bs)>>K N_(ue), finda N_(bs)×(N_(bs)−K N_(ue)) matrix G that satisfies H_(b-u)G=0 where 0 isa K N_(ue)×(N_(bs)−K N_(ue)) all-zero matrix. Then, in the downlinkdirection, using the BF matrixB _(di) =G(H _(b-s) G)⁺,  (3)where (H_(b-s)G)⁺ is the pseudo-inverse of (H_(b-s)G) and at leastN_(bs)>>K (N_(sc)+N_(ue)), the received signal y_(sc) by the SCs isgiven byy _(sc) =H _(b-s) B _(di) S _(d) x _(bs) +n _(sc) =S _(d) x _(bs) +n_(sc).  (4)But the interference y_(uei) received by the UEs due to BS→SCtransmission is given byy _(uei) =H _(b-u) B _(di) S _(d) x _(bs)=0  (5)because H_(b-u)G=0.

MFD-SC-IS achieves higher overall throughput than MFD-SC because theSignal to Interference and Noise Ratio (SINR) is higher for the UEs.However, this throughput gain comes with a cost: the interferencesuppression pre-coding matrix may affect the transmission power, andthere is additional overhead for estimating the CSI of the BS-UEchannels, i.e., the BS needs to estimate H_(b-u). When both BS and UEscan transmit and receives using the same frequency channel, the channelreciprocity can be used to reduce the overhead. Namely, a BS canestimate H_(b-u) by having a UE transmits pilot signals. Unlike the SCswhich are typically static, the UEs can be fast moving, thus, thechannel estimation may need to be repeated often due to the short BS-UEchannel coherence time. Thus, in one embodiment as shown in FIG. 2, theinterference from the MUBF transmission of a BS to a UE is estimated,i.e., the interference power P_(i) at the UE under the MUBF transmissionof the BS is estimated 8. Then the estimated P_(i) is compared with athreshold α 9. If the interference is smaller than the required value α,the BS uses MFD-SC with regards to this UE, i.e., the BS does notinclude this UE in the MFD-SC-IS pre-coding matrix 10; on the otherhand, if the interference is larger than a required value α, the BS usesMFD-SC-IS with regards to this UE, i.e., the BS includes this UE in theMFD-SC-IS pre-coding matrix 11.

The MFD-SC and MFD-SC-IS embodiments enable a new cellular architecturewith wireless backhaul SCs. Because the BSs use massive MIMO MUBF, eachBS can provide full bandwidth wireless link with many SCs simultaneouslyby spatial multiplexing and have BS-SC links with higher SINR than theBS-UE links. At the same time, each radio on the BS can be low powerbecause of massive MIMO power gain. MUBF reduces the interferences toother nodes. Since a SC is close to UEs in its range, the SINR of theSC-UE improves. As a result, analysis and data show that the MFD-SC andMFD-SC-IS embodiments offer significant throughput gain in both DL andUL directions over simple TDD based wireless backhaul where the BS-SCand SC-UE communications are separated in time, namely, when a BS sendsDL data to SCs, the SCs are not transmitting, and when SCs send data toUEs, the BS is not transmitting, vice versa, when a SCs send UL data tothe BS, the UEs are not transmitting, and when UEs send data to SCs, theSCs are not transmitting.

Analysis and data also show that when N_(bs) is sufficiently larger thanKN_(sc), the backhaul throughput with a SC in MFD-SC-IS or MFD-SC canmatch the throughput of the SCs, thus achieving the same effect of awired backhaul without requiring wired backhaul connections at the SCs.

In MFD-SC and MFD-SC-IS, there is also additional interferences in thenetwork that are not present in an prior art TDD wireless backhaul SCnetwork, namely, the interference on a SC's receiving of signal from aUE caused by another SC's transmission to a BS, the interference on aSC's receiving of signal from a BS caused by another SC's transmissionto a UE, and the interference on a BS's receiving of signal from SCscause by transmission of UEs to SCs. The last of the three can be dealtwith by the massive MIMO receive BF at the BS. In some cases, this UE toBS interference may be neglected when UE's signal is much weaker at BSthan the SC's signal at the BS, which is typically the reason for usingthe SC to serve the UE. The first two interferences, referred to asSC-SC interferences, may be reduced by having (a) the SCs sufficientlyfar apart or selecting sufficiently far apart SCs in a time slot toparticipate in MFD-SC, (b) using different frequencies segments orsubcarriers for the interfering BS-SC-UE links, or (c) using MIMO BF bythe SCs. The second case (b) is an embodiment further comprisingallocating a different frequency segment or set of subcarriers to eachBS-SC-UE(s) path that is causing significant SC-SC interference to eachother. The BS still communicate with a SC using the same frequencies asthe SC uses to communicate with its UEs, so each path is still the sameMFD-SC embodiment described above but neighboring BS-SC-UE(s) paths nolonger causes SC-SC interference because they use different frequencies.The latter case (c) is an embodiment further comprising one or more SCsthat use multiple antennas in its transmission to BF to the receivingnodes, either the BS or UE, which increase the SINR at the intendedreceiver and reduces the SC-SC interference.

For SCFD to function, the self-interference at a SCFD-SC must becanceled well, i.e., the interference caused by a SCFD-SC's Tx signal onits receiver must be canceled, ideally completely. But in practice, theself-interference is not completely canceled. The effect of incompletecancellation of self-interference on the MFD-SC and MFD-SC-ISembodiments were analyzed and the results show that even with incompletecancellation of self-interference, the MFD-SC and MFD-SC-IS embodimentsstill offer significant throughput gain in both DL and UL directionsover simple TDD, albeit less than with complete self-interferencecancellation.

The MFD-SC and MFD-SC-IS embodiments may further comprises having thechoice to use both wired backhaul SCs and wireless backhaul SCs in awireless network, and in areas where the BS-UE link is too weak tosupport high data rate, evaluating the BS-UE and BS-SC wireless link anddeciding whether to use the a wired backhaul SC or a wireless backhaulsmall cell. Furthermore, in an area a wireless backhaul SC can be used,the BS-UE interferences and SC-SC interferences is evaluated based onanalysis of the deployment and path loss assessment to decide whether touse a SCFD-SC or use different frequency resource blocks (FRBs) orAlmost Blank Subframes (ABSs) in different FRBs for BS-SC and SC-UEcommunications.

In prior art eICIC inter-cell interference control technology, when a SCis communicating with UE(s) in its range using a FRB, e.g., set ofsubcarriers, the BS uses ABS to communicate with other UEs to avoidinterfering with the SC-UE communication in the same FRB at the sametime. One embodiment of this invention modifies the above MFD-SCembodiment, instead of a SC simultaneously transmits and receives usingexactly the same frequencies, by allocating different FRBs orsubcarriers for the BS-SC communication and the SC-UE communication. Theoverall throughput will decrease compared with MFD-SC but it eliminatesthe need of suppression of BS to UE interference and SC-SCinterferences. This may still be considered in-band wireless backhaulbecause the FRBs allocated for BS-SC and SC-SC communications can all bein the same frequency band for a prior art TDD network. An SC in such anembodiment still needs to perform self-interference cancellation as theSC can transmit using a first set of FRB(s) that is right next to asecond set of FRB(s) over which the SC is receiving, without a frequencygap or with a very small frequency gap between the two sets to avoidwasting frequency resources. As a result, the SC's receiver must cancelthe strong interference from the SC's transmitting signal in the firstset of FRBs in order to receive the weaker signal from the BS or UE inthe second set of FRBs. This interference cancellation can be performedusing a RF filter to generate a RF cancellation signal that subtractsthe interfering signal in the first set of FRB(s). It may further becanceled by generating an analog cancellation signal in analog basebandor IF (intermediate frequency) to avoid saturating the ADC. In digitalbaseband, the subcarriers in the first set of FRB(s) can be simplyignored as the received signals are in the non-overlapping second set ofFRB(s).

In another embodiment, a BS with a large number of antennas, e.g.,N_(bs)=128, uses massive MIMO MUBF with a first ABS to transmitting toSCs to remove interference to UEs in SCs, and BS receives from SCs usingmassive MIMO MUBF while the neighboring SCs use a second ABS to avoid SCto SC interference on one SC's receiving of a signal from its UE due totransmission from a neighboring SC. The first ABS is over the FRB(s)used by the SCs to transmitting to their UEs. The second ABS is over theFRB(s) used by the UEs in neighboring SCs to transmit to their SCs.

The embodiments for mitigating the SC-SC interferences may furtherinclude scheduling and coordination among SCs in each other'sinterference range using either frequency or time resource blocksdepending on the properties of the BS, SCs and UEs, the conditions ofthe channels, the data traffic requirements such as delay and jitter,and/or the availability of the frequency resources. When small delay orsmall jitter is required, maintaining continuous data transmissionbetween BS-SC using one FRB and continuous data transmission betweenSC-UE using another FRB is more advantageous.

When Frequency Division Duplex (FDD) is used for the BS, SC and UE, theMFD-SC embodiment can be modified so that when a BS receives UL withMUBF from SCs using a first frequency band F1 12, the SCs are receivingUL from their UEs using the same frequency band F1, and reversely, atthe same time, BS transmits DL with MUBF to SCs using a second frequencyband F2 13 while SCs are transmitting DL to their UEs using the samefrequency band F2, as shown in FIG. 3. A SC in this embodiment has twoor two sets of SCFD radios, one performing self-interference cancelationat F1 and the other performing self-interference cancelation at F2. BSs,SCs and UEs in such an embodiment are all FDD apparatus and the effectis superimposing the two time instances in FIGS. 1A and 1B together inthe same time instance.

In another FDD embodiment, the direction of F1 and F2 are reversed inthe SC-UE link and the network traffic is separated using time division,as shown in FIGS. 4A and 4B. BSs, SCs and UEs in such an embodiment areall FDD apparatus with the BS and UE using F1 to receive and F2 totransmit but the SC using F1 to transmit and F2 to receive. Thisembodiment has the advantage that it eliminates the BS-UE and SC-SCinterferences and it does not require SCFD. The throughput is reducedbut the complexity is also lowered. People skilled in the art can seethat other combinations of the FDD and TDD can be obtained withdifferent tradeoff on throughput and complexity. Note that when a SC istransmitting to or receiving from multiple UEs, different frequencies orsubcarriers in the band can be used for each UE.

Although the foregoing descriptions of the preferred embodiments of thepresent inventions have shown, described, or illustrated the fundamentalnovel features or principles of the inventions, it is understood thatvarious omissions, substitutions, and changes in the form of the detailof the methods, elements or apparatuses as illustrated, as well as theuses thereof, may be made by those skilled in the art without departingfrom the spirit of the present inventions. Hence, the scope of thepresent inventions should not be limited to the foregoing descriptions.Rather, the principles of the inventions may be applied to a wide rangeof methods, systems, and apparatuses, to achieve the advantagesdescribed herein and to achieve other advantages or to satisfy otherobjectives as well.

What is claimed is:
 1. A method for wireless networking comprising one or more base stations (BSs) with N_(bs) antennas; two or more small cells (SCs) in the range of each of said one or more base stations, wherein each of said two or more small cells has N_(sc) antennas, and uses N_(sc1)≦N_(sc) antennas for communication with said BS in the range and uses N_(sc2)≦N_(sc) antennas for communication with one or more user equipment (UEs); which comprises: at the same time a BS selected from said one or more BSs is transmitting downlink (DL) signals to K SCs selected from said two or more SCs in the range thereof using multi-user transmit beamforming (BF) in a DL frequency channel where K>1 and N_(bs)≧KN_(sc1), a SC selected from said K SCs receiving the DL signals from said BS and simultaneously transmitting DL signals to one or more UEs in its range using the same DL frequency channel in a single-channel full duplex mode and performing cancelation of an interference from the transmission of the DL signals to the one or more UEs on the receiving of the DL signals from the BS, and canceling the remaining interference after an Analog to Digital Converter in digital baseband using digital signal processing; and at the same time said BS selected from said one or more BSs is receiving uplink (UL) signals from said K SCs using multi-user receive BF in a UL frequency channel where K>1 and N_(bs)≧KN_(sc1), said SC selected from said K SCs transmitting the UL signals to said BS simultaneously receiving UL signals from said one or more UEs in its range using the same UL frequency channel in a single-channel full duplex mode and performing cancelation of an interference from the transmission of the UL signals to the BS on the receiving of the UL signals from the one or more UEs, and canceling the remaining interference after an Analog to Digital Converter in digital baseband using digital signal processing.
 2. The method in claim 1, wherein said BS selected from said one or more BSs selects the number of BS antennas to use such that said number is sufficiently larger than the total number of antennas on said K SCs communicating with said BS using the same frequency resource to match the throughput of the link between said BS and said K SCs with the sum throughput of said K SCs.
 3. The method in claim 1 further comprising canceling self-interference using a RF filter that generates a RF cancelation signal to subtract the self-interference from the received RF signal prior to the Low Noise Amplifier of the receiver.
 4. The method of claim 1 further comprising canceling self-interference that exists after the Low Noise Amplifier by generating an analog cancelation signal in analog baseband or IF (intermediate frequency) prior to Analog to Digital Converter.
 5. The method in claim 1, further comprising using the same antennas on at least one of said K SCs simultaneously for DL and UL with N_(sc)=N_(sc1)=N_(sc2) for said at least one of said K SCs.
 6. The method in claim 1 further comprising transmitting DL signals from said SC selected from said K SCs to at least one of said one or more UEs in its range using a first frequency channel at one time slot and receiving UL signals from said at least one UE(s) using the same first frequency channel at another time slot in a Time-Division Duplexing network.
 7. The method in claim 6 further comprising the BS selected from said one or more BSs estimating the channel matrix of the channels between the BS and the two or more SCs H_(b-s) by having the SCs transmits UL pilot signals, and using channel reciprocity to estimate the downlink channel from the BS to the SCs.
 8. The method in claim 1 further comprising simultaneously, via SCs, transmitting DL signals to one or more UEs in its range using a first frequency channel and receiving UL signals from said one or more UEs using a second frequency channel in a Frequency-Division Duplexing network.
 9. The method in claim 1 further comprising suppressing the interference of the BS to SC transmission to the SC to UE transmission by adding a null space pro-coding matrix to the BS to SC transmission.
 10. The method in claim 9 further comprising estimating the interference power P_(i) at a UE under the multi-user beamforming (MUBF) transmission of the BS, comparing the estimated P_(i) with a threshold α, and if the interference is larger than a required value α, the BS including this UE in the interference suppression pre-coding matrix.
 11. The method in claim 1 further comprising allocating a different frequency segment or set of subcarriers to each BS-SC-UE(s) path that is causing significant inter-SC interference.
 12. The method of claim 1 further comprising beamforming in DL from BS to UEs or UL from UEs to BS using the antennas of one or more SCs to reduce the inter-SC interference.
 13. The method of claim 12 wherein the beamforming pre-coding computation is performed at one or more of the SCs.
 14. The method of claim 12 wherein the beamforming pre-coding computation is performed at the BS.
 15. The method in claim 1 further comprising using both wired backhaul to some SCs and wireless backhaul to other SCs in a wireless network.
 16. The method in claim 1 further comprising using one frequency channel for wireless link between a BS and a SC and a different frequency channel for wireless link between a SC and a UE.
 17. An apparatus for wireless networking comprising a baseband and radio frequency components supporting N_(sc) antennas, wherein the apparatus uses N_(sc1)≦N_(sc) antennas for communication with a BS with N_(bs) antennas and uses N_(sc2)≦N_(sc) antennas for communication with one or more UEs in its range; wherein the apparatus communicates wirelessly with a BS; wherein, at the same time a BS is transmitting DL signals to the apparatus using multi-user transmit BF in a DL frequency channel where N_(bs)≧KN_(sc1), the apparatus operates in single-channel full duplex mode by simultaneously transmitting DL signals to said one or more UEs in its range using the same DL frequency channel and receiving the DL signals from the said BS and performing cancelation of the interference from the transmission of the DL signals to the one or more UEs on the receiving of the DL signals from the said BS, and canceling the remaining interference after an Analog to Digital Converter in digital baseband using digital signal processing; and at the same time the BS is receiving UL signals from the apparatus using multi-user receive BF in a UL frequency channel where N_(bs)≧KN_(sc1), the apparatus operates in single-channel full duplex mode by simultaneously receiving UL signals from the one or more UEs in its range using the same UL frequency channel and transmitting the UL signals to said BS, and performing cancelation of the interference from the transmission of the UL signals to said BS on the receiving of the UL signals from the one or more UEs, and canceling the remaining interference after an Analog to Digital Converter in digital baseband using digital signal processing. 